Feudalism and the Manor relations were based on the social classes, because of since the fall of the Roman Empire owners of the lands created a series of towns that were protected by heavy walls and since poor people needed protection from the Barbaric invasions, they worked for the landlords.
That said, social structures were strict and it was very uncommon for a person to move from being a peasant to being a landlord, because the social structure was made to prevent that.
